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Published online by Cambridge University Press: 02 September 2010
The effects of long-term oral administration of enkephalinase inhibitors (acetorphan and thiorphan) on food and water intake, live-weight gain and food conversion efficiency were investigated in growing rats and mice. In rats, daily drenching with acetorphan (an absorbable prodrug of thiorphan) at 1 mg/kg per day for 8 days did not alter food and water consumption but significantly increased live-weight gain (32·0 (s.d. 5·1) g for control rats v. 40·7 (s.d. 9·1) g for treated rats (P ≤ 0·05 U test) and improved food conversion efficiency (4·37 (s.d. 0·49) g food per g gain for control rats v. 3·70 (s.d. 0·67) g food per g gain for treated rats). In mice, lower doses (0·2 mg/kg per day) of thiorphan and acetorphan given in the drinking water similarly affected live-weight gain (7·7 (s.d. 0·9) g v. 6·0 (s.d. 1·6) g in 3-week-old mice receiving thiorphan and 2·6 (s.d. 0·4) g in 5-week-old mice receiving acetorphan) with a likely improvement in food conversion efficiency. These results suggest that oral administration of enkephalinase inhibitors may alter growth in rodents, probably by affecting the digestive process.